1. Field of the Invention
The present invention relates to hydraulic-pneumatic flotation appartus and more particularly to improvements therein for increasing efficiency of operation.
2. Description of the Prior Art
Commerically valuable minerals, for example, metal sulfides, apatitic phosphates and the like, are commonly found in nature mixed with relatively large quantities of gangue materials, and as a consequence it is usually necessary to beneficiate the ores in order to concentrate the mineral content thereof. Mixtures of finely divided mineral particles and finely divided gangue particles can be separated and a mineral concentrate obtained therefrom by well known froth flotation techniques. Broadly speaking, froth flotation involves conditioning an aqueous slurry or pulp of the mixture of mineral and gangue particles with one or more flotation reagents which will promote flotation of either the mineral or the gangue constituents of the pulp where the pulp is aerated. The conditioned pulp is aerated by introducing into the pulp a plurality of minute air bubbles which tend to become attached either to the mineral particles or to the gangue particles of the pulp, thereby causing these particles to rise to the surface of the body of pulp and form thereat a float fraction which overflows or is withdrawn from the flotation apparatus.
Typical of such flotation apparatus for accomplishing the foregoing is that disclosed in U.S. Pat. No. 3,371,779. In such apparatus, the conditioned pulp is introduced into a flotation compartment containing a relatively quiescent body of an aqueous pulp, and aerated water is introduced into the lower portion of the flotation compartment through orifices formed in the bottom wall of the flotation compartment. A body of aerated water is established in a hydraulic compartment disposed directly below the flotation compartment by introducing air and water into the hydraulic compartment while simultaneously dispersing a multitude of fine air bubbles throughout the water in the hydraulic compartment. The body of aerated water in the hydraulic compartment is in fluid communication with the aqueous pulp in the lower portion of the flotation compartment through the aforementioned orifices formed in the bottom wall of the flotation compartment. An overflow fraction containing floated particles of the pulp is withdrawn from the top of the body of aqueous pulp and an underflow or non-float fraction containing non-floated particles of the pulp is withdrawn from the pulp in the lower portion of the flotation compartment.
In a modification of such apparatus, the underflow of non-float fraction is withdrawn from the central portion of the bottom wall of the flotation compartment by means of a discharge pipe opening through the wall. By reason of the discharge opening being in the central portion of this bottom wall, otherwise referred to as a constriction plate, for certain sized flotation compartments, in inefficiency in operation results due to the non-uniformity in aeration in the flotation compartment immediately above the constriction plate and more particularly in the vicinity of the discharge opening. Due to the absence of aeration immediately above the discharge opening, the particulate matter, including the float fraction tends to recirculate and discharge through the opening. This results, then, in the loss of some of the desired float fraction of mineral.
A further problem encountered involves the removal of coarse and heavy particles of ore contained in coarse feed of a size of about plus 14 mesh. With the constriction plate being flat and horizontally disposed, the coarse particles tend to settle and to collect onto the constriction plate thereby forming a relatively thick bed. This bed overlies and at least partially plugs the orifices thereby inhibiting the passage of aerated water and more particularly tiny air bubbles into the flotation chamber. Instead, the tiny bubbles combine internally of the bed and release in the form of relatively large bubbles which defeat the flotation function. In order to restore proper aeration of tiny bubbles rising in the flotation chamber, the bed of agglomerated material must be removed, requiring in some instances equipment shut-down.
Other prior art relating to the concentration of minerals is disclosed in U.S. Pat. Nos. 2,753,045, 2,758,714 and 3,298,519.